Abdominal Cuticle Research Articles

The ATP-binding cassette transporter subfamily G member 4 mediates cuticular hydrocarbon transport to regulate drought tolerance in Acyrthosiphon pisum

ABC transporters are a highly conserved membrane protein class that promote the transport of substances across membranes. Under drought conditions, insects primarily regulate the content of cuticular hydrocarbon (CHC) to retain water and prevent evaporative loss. Involvement of ABC transporter protein G (ABCG) subfamily genes in insect CHC transport has been relatively understudied. In this study, we demonstrated that ABCG4 gene in Acyrthosiphon pisum (ApABCG4) is involved in CHC transport and affects drought tolerance by regulating CHC accumulation. ApABCG4 is strongly expressed in the abdominal cuticle and embryonic stages of A. pisum. Effective silencing of ApABCG4 was achieved using RNAi, and the silencing duration was analyzed. ApABCG4 silencing resulted in a significant decrease in the total and component contents of the CHC and cuticular waxy coatings of A. pisum. Nevertheless, the internal hydrocarbon content remained unchanged. The lack of cuticular hydrocarbons significantly reduced the drought tolerance of A. pisum, shortening its survival time under drought stress. Drought stress caused significant upregulation of ApABCG4. Molecular docking showed that ApABCG4 has a high binding affinity for nine n-alkanes of CHC through electrostatic interactions. These results indicate that ApABCG4 is a novel RNAi target with key applications in aphid biological control.

An optimized artificial blood feeding assay to study tick cuticle biology

Ticks, ectoparasitic arachnids, are prominent disease vectors impacting both humans and animals. Their unique blood-feeding phase involves significant abdominal cuticle expansion, sharing certain similarities with insects. However, vital aspects, including the mechanisms of cuticle expansion, changes in cuticular protein composition, chitin synthesis, and cuticle function, remain poorly understood. Given that the cuticle expansion is crucial for complete engorgement of the ticks, addressing these knowledge gaps is essential. Traditional tick research involving live animal hosts has inherent limitations, such as ethical concerns and host response variability. Artificial membrane feeding systems provide an alternative approach, offering controlled experimental conditions and reduced ethical dilemmas. These systems enable precise monitoring of tick attachment, feeding parameters, and pathogen acquisition. Despite the existence of various methodologies for artificial tick-feeding systems, there is a pressing need to enhance their reproducibility and effectiveness. In this context, we introduce an improved tick-feeding system that incorporates adjustments related to factors like humidity, temperature, and blood-feeding duration. These refinements markedly boost tick engorgement rates, presenting a valuable tool for in-depth investigations into tick cuticle biology and facilitating studies on molting. This refined system allows for collecting feeding ticks at specific stages, supporting research on tick cuticle biology, and evaluating chemical agents' efficacy in the engorgement process.

A fatty acid anabolic pathway in specialized-cells sustains a remote signal that controls egg activation in Drosophila.

Egg activation, representing the critical oocyte-to-embryo transition, provokes meiosis completion, modification of the vitelline membrane to prevent polyspermy, and translation of maternally provided mRNAs. This transition is triggered by a calcium signal induced by spermatozoon fertilization in most animal species, but not in insects. In Drosophila melanogaster, mature oocytes remain arrested at metaphase-I of meiosis and the calcium-dependent activation occurs while the oocyte moves through the genital tract. Here, we discovered that the oenocytes of fruitfly females are required for egg activation. Oenocytes, cells specialized in lipid-metabolism, are located beneath the abdominal cuticle. In adult flies, they synthesize the fatty acids (FAs) that are the precursors of cuticular hydrocarbons (CHCs), including pheromones. The oenocyte-targeted knockdown of a set of FA-anabolic enzymes, involved in very-long-chain fatty acid (VLCFA) synthesis, leads to a defect in egg activation. Given that some but not all of the identified enzymes are required for CHC/pheromone biogenesis, this putative VLCFA-dependent remote control may rely on an as-yet unidentified CHC or may function in parallel to CHC biogenesis. Additionally, we discovered that the most posterior ventral oenocyte cluster is in close proximity to the uterus. Since oocytes dissected from females deficient in this FA-anabolic pathway can be activated in vitro, this regulatory loop likely operates upstream of the calcium trigger. To our knowledge, our findings provide the first evidence that a physiological extra-genital signal remotely controls egg activation. Moreover, our study highlights a potential metabolic link between pheromone-mediated partner recognition and egg activation.

Juvenile hormone inhibits adult cuticle formation in Drosophila melanogaster through Kr-h1/Dnmt2-mediated DNA methylation of Acp65A promoter.

Differentiation of imaginal epidermal cells of Drosophila melanogaster to form adult cuticles occurs at approximately 40-93 h after puparium formation. Juvenile hormone (JH) given at pupariation results in formation of a second pupal cuticle in the abdomen instead of the adult cuticle. Although the adult cuticle gene Acp65A has been reported to be down-regulated following JH treatment, the regulatory mechanism remains unclear. Here, we found that the JH primary response gene Krüppel homologue 1 (Kr-h1) plays a vital role in the repression of adult cuticle formation through the mediation of JH action. Overexpression of Kr-h1 mimicked-while knocking down of Kr-h1 attenuated-the inhibitory action of JH on the formation of the adult abdominal cuticle. Further, we found that Kr-h1 inhibited the transcription of Acp65A by directly binding to the consensus Kr-h1 binding site (KBS) within the Acp65A promoter region. Moreover, the DNA methyltransferase Dnmt2 was shown to interact with Kr-h1, combined with the KBS to promote the DNA methylation of sequences around the KBS, in turn inhibiting the transcription of Acp65A. This study advances our understanding of the molecular basis of the "status quo" action of JH on the Drosophila adult metamorphosis.

Oviposition Behavior of the Bed Bug, Cimex lectularius (Hemiptera: Cimicidae)

Female bed bugs, Cimex lectularius, in strains from three widely separated geographic regions were evaluated for diel and daily periodicity in oviposition, as well as for the duration of oviposition per se and apparent egg marking behavior. Females that were mated and fed for the first time and laying their first clutch of eggs and females fed a second time before laying their second clutch of eggs both oviposited preferentially in the scotophase of a 14:10 L:D cycle. Oviposition began before the photophase ended, indicating it was not induced by the onset of darkness and suggesting that oviposition may be governed by a circadian rhythm. First-clutch females began to oviposit closer to the onset of darkness and 1–2 days later than second-clutch females, respectively, suggesting that first-clutch females were more strictly entrained to the L:D cycle and were still undergoing reproductive maturation. In all cases, oviposition of one clutch was finished by day 10, but the frequency distributions of eggs laid daily by first-clutch and second-clutch females, as well as those of females from the three different strains, were all significantly different. The acts of oviposition and subsequent apparent egg marking behavior (a novel observation) lasted mean durations of 4.7 s and 24.1 s, respectively. During apparent egg marking, a female would repeatedly touch the abdominal cuticle in the region of the scent glands with her metathoracic tarsi and then touch the newly laid egg while concurrently waving the tip of her abdomen back and forth across the surface of the egg.

Toxicity and synergistic activity of compounds from essential oils and their effect on detoxification enzymes against Planococcus lilacinus.

Mealybug, Planococcus lilacinus Cockerell, is a primary surface-feeding insect pest of fruit and flowering plants and also transmits plant viruses, resulting in economic crop loss. Inappropriate and recurrent use of pesticides for mealybug control results in resistance building and deleterious effects on humans and the environment. Essential oils are the most excellent choice for insecticides. Insecticidal activities of pure compounds of essential oils against P. lilacinus are not reported. The present study aims to study the insecticidal activities of some pure active compounds and their binary mixture's action by topical application against P. lilacinus. Results showed that the pure compounds of L-limonene, β-myrcene, and ocimene revealed toxicity (each at LD50 = 0.37 µg/insect) after 96h. The binary mixtures of geraniol + L-menthol and L-limonene + geraniol exhibited synergistic effects (each at LD50 = 0.03 µg/insect) after 96h. The monoterpenes of ocimene and β-myrcene at the higher concentration of 5,000 ppm substantially inhibited the detoxification enzyme activities of AChE (0.93 and 0.78 mU/mg, respectively) and GST (2.19 and 7.29 nmol/min/ml, respectively) in P. lilacinus after 48h. SEM analysis reported the significant anomalies on the morphology of abdominal cuticle, setae, and thoracic leg after 96-h treatment with ocimene at 1,250 ppm against P. lilacinus. Based on the results, the tested pure compounds and their combinations can be suggested for the control of mealybugs.

RNAi Suppression of Hormone Receptor HR3 Blocks Larval Molting and Metamorphosis in the Cigarette Beetle, Lasioderma serricorne

Hormone receptor 3 (HR3), an early-late gene of the 20-hydroxyecdysone (20E) signaling pathway, plays a critical role in insect metamorphosis and development. In this study, we identified and characterized an HR3 gene (LsHR3) from the cigarette beetle, Lasioderma serricorne. The open reading frame of LsHR3 is 1581 bp encoding a 527 amino acid protein that contains a conserved DNA binding domain and a ligand binding domain. LsHR3 was mainly expressed in the fourth-instar larvae, prepupae, and pupae and showed high expression in the fat body. The expression of LsHR3 was induced by 20E, while it was significantly suppressed by silencing of six 20E synthesis and signaling pathway genes. RNA interference (RNAi)-aided knockdown of LsHR3 in the fourth-instar larvae disrupted the larval–pupal molting and caused 100% mortality. The 20E titer of LsHR3-depletion larvae was decreased, and expressions of five 20E synthesis genes were dramatically decreased. Silencing LsHR3 reduced chitin content and downregulated the expression of genes involved in chitin synthesis and degradation. Hematoxylin and eosin staining of abdominal cuticle showed that no apolysis occurred after silencing LsHR3. These results suggest that LsHR3-mediated 20E signaling is involved in the regulation of chitin metabolism during the molting process of L. serricorne, and targeting this gene by RNAi has potential in controlling this pest.

Tyrosine hydroxylase involved in cuticle tanning and reproduction in the 28-spotted potato ladybeetle, Henosepilachna vigintioctopunctata.

Tyrosine hydroxylase (TH), a melanin synthesis pathway enzyme hydroxylating tyrosine into 3,4-dihydroxyphenylalanine, is involved in the pigmentation and sclerotization of insect cuticles. However, the role of TH in 28-spotted potato ladybeetle (Henosepilachna vigintioctopunctata), an emerging pest of the solanaceous crops has been explored to a limited extent. In this study, we integrated dietary RNA interference (RNAi) and hematoxylin and eosin (H&E) staining with various bioassays to analyze the role of tyrosine hydroxylase (HvTH) throughout the developmental processes of Henosepilachna vigintioctopunctata. The results revealed that ingestion of dsHvTH led to cuticle tanning impairment, arrested larval feeding in the first and second instars of Henosepilachna vigintioctopunctata, and subsequently resulted in 100% mortality. The H&E staining assays revealed that dsHvTH prevented new abdominal cuticle formation. A pharmacological study using 3-iodo-tyrosine (3-IT), a HvTH inhibitor, disrupted larval-larval-pupal cuticle tanning during the third-fourth instar larval development and eventually failed to pupate. Similarly, dsHvTH fed to fourth instars hindered larval-pupal-adult cuticle tanning, and the eclose adults were 100% malformed. Ingestion of dsHvTH or 3-IT significantly down-regulated HvTH, HvDDC, Hvebony, and Hvlaccase2 expression and reduced dopamine levels. Finally, HvTH silencing in adult females substantially reduced the offspring hatching rates. The collective results of the study suggested that HvTH plays conserved roles in larval-pupal-adult cuticle melanization and sclerotization while exhibiting a novel function in Henosepilachna vigintioctopunctata reproduction. © 2022 Society of Chemical Industry.

RR-1 cuticular protein TcCPR69 is required for growth and metamorphosis in Tribolium castaneum.

Cuticle is not only critical for protecting insects from noxious stimuli but is also involved in a variety of metabolic activities. Cuticular proteins (CPs) affect cuticle structure and mechanical properties during insect growth, reproduction, and environmental adaptation. Here, we describe the identification and characterization of a member of the RR-1 subfamily of CPs with an R&R consensus (CPR) in Tribolium castaneum (TcCPR69). Although it was previously reported to be highly expressed in the wings, we found that knocking down TcCPR69 by RNA interference (RNAi) did not cause obvious wing abnormalities but markedly disrupted the growth and metamorphosis of beetles with 100% cumulative mortality; additionally, the chitin content of the pharate adult was decreased and the new abdominal cuticle was significantly thinner before molting. TcCPR69 showed chitin-binding ability and the expression levels of key genes involved in chitin metabolism (trehalase [TcTRE], chitin synthase [TcCHSA and TcCHSB], and chitinase [TcCHT5 and TcCHT10]) were also decreased by TcCPR69 knockdown. TcCPR69 gene expression peaked shortly after molting and was increased 2.61 fold at 12 h after 20-hydroxyecdysone (20E) injection. This was reversed by RNAi of the ecdysone-related genes ecdysone receptor (TcECR) and fushi tarazu transcription factor 1 (TcFTZ-F1). These results indicate that TcCPR69 is positively regulated by 20E signaling to contribute to cuticle formation and maintain chitin accumulation during the growth and metamorphosis of beetles.

A CYP380C10 gene is required for waterproofing and water retention in the insect integument

Cuticular hydrocarbons (CHCs) are important components in the integument of insects and are required for development and survival. Insect-specific CYP4G subfamily, of the P450 enzymes, catalyze the oxidative decarbonylation step in the biosynthesis of CHCs. Here, we characterized CYP380C10 gene function in a Hemiptera rice pest, Nilaparvata lugens. We used RNA interference–mediated expression silencing to reveal that NlCYP380C10 played a key role in waterproofing and water–retention in the integument of N. lugens. Knockdown of NlCYP380C10 significantly reduced body weight and caused mortality. Scanning electron microscopy showed the loss of the lipid layer on the surface of the abdominal cuticle of the dsNlCYP380C10-injected adults. Furthermore, CHC profile analysis revealed that NlCYP380C10 knockdown significantly decreased the amounts of CHCs in adult females. This suggested that NlCYP380C10 was involved in CHC biosynthesis. Reduction of CHC content caused the loss of the intact lipid layer of the cuticle, which resulted in loss of the waterproofing and water-retention functions. This led to failure of molting and eclosion. Our findings expanded the knowledge of CHC biosynthesis in the insect integument and led to a better understanding of the functional roles of CYP450 genes involved in waterproofing and water–retention in insects.

CPR Gene Contributes to Integument Function and Ovary Development in a Rice Planthopper.

Nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome P450 reductase (CPR) is an essential enzyme that transfers electrons from NADPH to cytochrome P450 monooxygenases. CPR is involved in cuticular hydrocarbon (CHC) synthesis in insects and is vital for insect development and survival. Here, we clarify the physiological function of a CPR gene in Nilaparvata lugens, an important rice pest, by using RNA interference. CPR gene knockdown leads to the functional loss of waterproofing and water retention in the integument of female adults, which causes significantly reduced body weight and a lethal phenotype. Scanning electron microscopy shows that the lipid layer on the outermost surface of the abdominal cuticle becomes thin in dsCPR-injected adults. Furthermore, CHC profile analysis reveals that CPR knockdown significantly decreases the contents of CHCs with a carbon chain length ≥ C27 in adult females. Moreover, we find that CPR knockdown generates a deficient phenotype in ovaries with deformed oocytes and a complete failure of egg-laying. These findings suggest that CPR plays multiple functional roles in CHC biosynthesis and embryo development in insects.

Vacuolar (H+ )-ATPase subunit c is essential for the survival and systemic RNA interference response in Locusta migratoria.

Vacuolar (H+ )-ATPase (V-ATPase) is a multi-subunit enzyme that hydrolyzes adenosine triphosphate (ATP) to transport protons across a cellular membrane, and it plays an important role in numerous biological processes, including in growth, development and immune responses. The c subunit of V-ATPase is a highly conserved subunit of the rotatory proteolipid ring that is required for binding and transporting protons. To date, there are only a few published reports on V-ATPase-c functions in insects. We identified and characterized the V-ATPase-c gene in Locusta migratoria, one of the most destructive agricultural insect pests in the world. LmV-ATPase-c was predominately expressed in Malpighian tubules of nymphs, followed by the hindgut and ovary, while the other tissues showed relatively low expression levels. Silencing of LmV-ATPase-c caused severe molting defects in nymphs and a high mortality rate of > 90%. Histological staining and microscopic examination of sections from the abdominal cuticle revealed the absence of newly formed cuticle in nymphs that were injected with dsLmV-ATPase-c. In addition, silencing of LmV-ATPase-c transcript levels significantly impaired RNA interference (RNAi) efficiency of a reporter gene. By quantifying double-stranded RNA (dsRNA) amounts by quantitative polymerase chain reaction (PCR), we found that RNAi against LmV-ATPase-c provoked a dramatic accumulation of dsRNA in the endosomes of epidermal and midgut cells of Locusta migratoria. Our results indicate that LmV-ATPase-c is indispensable for the formation of new cuticle during the molting process and has pivotal functions in dsRNA escape from endosomes. LmV-ATPase-c might be a valuable target for developing new strategies for insect pest management. © 2022 Society of Chemical Industry.

Downregulation of NADPH-cytochrome P450 reductase via RNA interference increases the susceptibility of Acyrthosiphon pisum to desiccation and insecticides.

Nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome P450 reductase (CPR) is involved in the metabolism of endogenous and exogenous substances, and detoxification of insecticides. RNA interference (RNAi) of CPR in certain insects causes developmental defects and enhanced susceptibility to insecticides. However, the CPR of Acyrthosiphon pisum has not been characterized, and its function is still not understood. In this study, we investigated the biochemical functions of A. pisum CPR (ApCPR). ApCPR was found to be transcribed in all developmental stages and was abundant in the embryo stage, and in the gut, head, and abdominal cuticle. After optimizing the dose and silencing duration of RNAi for downregulating ApCPR, we found that ApCPR suppression resulted in a significant decrease in the production of cuticular and internal hydrocarbon contents, and of cuticular waxy coatings. Deficiency in cuticular hydrocarbons (CHCs) decreased the survival rate of A. pisum under desiccation stress and increased its susceptibility to contact insecticides. Moreover, desiccation stress induced a significant increase in ApCPR mRNA levels. We further confirmed that ApCPR participates in CHC production. These results indicate that ApCPR modulates CHC production, desiccation tolerance, and insecticide susceptibility in A. pisum, and presents a novel target for pest control.

Exoskeleton ageing and its relation to longevity and fecundity in female Australian leaf insects (

Senescence is a decline in reproduction and survival rate with advancing age resulting from deterioration of somatic tissues and systems throughout the body. Age-related somatic changes (somatic ageing) have been studied extensively in vertebrates but are less well known in other animals, including insects. Since adult insects have very limited ability to repair their exoskeleton, somatic ageing could involve deterioration and discolouration of the cuticle. We investigated age-related changes in wing pigmentation and abdominal cuticle necrosis in females of the Australian leaf insect Phyllium monteithi. Adult females varied markedly in the extent and pattern of pigmentation on their bodies, and we found that pigment spots on the forewings increased in size with age in most individuals. As females aged, most individuals also exhibited increasing levels of abdominal cuticle necrosis, resulting in the loss of abdominal cuticle along the margin of the abdomen. Neither the extent of pigmentation nor cuticle loss were clearly associated with reduced fecundity or longevity in the protected laboratory environment, but it remains unknown whether these age-related changes have functional implications in the wild. Our results show that the P. monteithi exoskeleton undergoes complex changes with age, with potential implications for functional traits and fitness.

RNAi suppression of the nuclear receptor FTZ-F1 impaired ecdysis, pupation, and reproduction in the 28-spotted potato ladybeetle, Henosepilachna vigintioctopunctata

Fushi-tarazu factor 1 (FTZF1) is an ecdysone-inducible transcription factor that plays a vital role during the metamorphosis in insects. In this study, we functionally characterized HvFTZ-F1 in H. vigintioctopunctata, a dreadful solanaceous crop pest, by using a dietary RNA interference technique. The HvFTZ-F1 expression levels were elevated in the 1st and 2nd-instars before molting and declined immediately after ecdysis. The HvFTZ-F1 silencing led to high mortality in the 1st instars, while the expression of the osmosis-regulative gene, HvAQPAn.G, was significantly increased in the 1st instars. HvFTZ-F1 silencing downregulated the Halloween and 20E-related genes, decreased the ecdysteroids titer, suppressed the expression of pigmentation-related genes, and reduced the catecholamines titer. In the 4th instars, HvFTZ-F1 silencing caused 100% mortality by arresting the development at the prepupal stage and preventing new abdominal cuticle formation. In the female adults, HvFTZ-F1 silencing caused an evident decrease in fecundity, prolonged the pre-oviposition period, reduced the number of eggs and hatching rate, severely atrophied the ovaries. Moreover, the 20E-related genes and the dopamine synthesis genes were suppressed in the dsHvFTZ-F1-treated females. Overall, our results revealed that HvFTZ-F1 regulates ecdysis, pupation, and reproduction in H. vigintioctopunctata, thereby could be a promising molecular target for the development of RNAi-based biopesticides to control H. vigintioctopunctata.

Bio efficacy of Cinnamaldehyde from <em>Cinnamomum verum</em> essential oil against <em>Culex quinquefasciatus</em> (Diptera: Culicidae)

This research aims to study the efficacy of Cinnamomum verum (Cv) extracts for ovicidal, larvicidal, and repellent activities against Culex quinquefasciatus mosquito vectors. The active components of C. verum or cinnamon oil by Gas Chromatography (GC) analysis showed the highest cinnamaldehyde at 83.53%. For ovicidal assay, C. verum essential oil at concentrations 12.5, 25 and 50 ppm at 72 h had 100% egg hatch inhibition and had a significant difference when compared to the control group (p<0.05). Larvicidal activity showed that concentrations of 25 and 50 ppm were highly effective in killing 100% mosquito larvae. Morphological changes in egg raft showed a faded color and eggs that seemed to have split from their raft while the larvae changed to a pale white wrinkled body with a destroyed inner tube of the body and were motionless. A Scanning electron microscope study showed that the eggshell and micropyle were wrinkled with the chitin peeled out. After treatment with cinnamon oil, larvae appeared to have a wrinkled body, the thorax and abdominal cuticle were also destroyed with high density of oil particles observed on mouth brushes and obstructing the spiracle. The repellent assay showed that cinnamon oil could repel both male and female mosquitos for up to 180 min. From the results, it was concluded that cinnamon oil had highly effective repellency against Culex quinquefasciatus adults and insecticidal activity on eggs and larvae stages evidenced by LC50 at 6.59±0.54, 9.07±0.67 and 36.91±7.56 ppm and its morphological changes indicated how the mosquito could not survive after cinnamon oil treatment hence this may be a useful alternative method that is green friendly for controlling mosquitoes in endemic areas.

Spn-A/rad51 mutant exhibits enhanced genomic damage, cell death and low temperature sensitivity in somatic tissues.

Homologous recombination (HR) is one of the key pathways to repair double-strand breaks (DSBs). Rad51 serves an important function of catalysing strand exchange between two homologous sequences in the HR pathway. In higher organisms, rad51 function is indispensable with its absence leading to early embryonic lethality, thus precluding any mechanistic probing of the system. In contrast, the absence of Drosophila rad51 (spn-A/rad51) has been associated with defects in the germline, without any reported detrimental consequences to Drosophila somatic tissues. In this study, we have performed a systematic analysis of developmental defects in somatic tissues of spn-A mutant flies by using genetic complementation between multiple spn-A alleles. Our current study, for the first time, uncovers a requirement for spn-A in somatic tissue maintenance during both larval and pupal stages. Also, we show that spn-A mutant exhibits patterning defects in abdominal cuticle in the stripes and bristles, while there appear to be only subtle defects in the adult wing and eye. Interestingly, spn-A mutant shows a discernible phenotype of low temperature sensitivity, suggesting a role of spn-A in temperature sensitive cellular processes. In summary, our study describes the important role played by spn-A/rad51 in Drosophila somatic tissues.

Involvement of apolipoprotein D in desiccation tolerance and adult fecundity of Acyrthosiphon pisum

Apolipoprotein D (ApoD) is a lipocalin superfamily member that plays important roles in the transport of small hydrophobic molecules, lipid metabolism, and stress resistance. Cuticular hydrocarbons are the principal components of the epicuticular lipid layer and play a critical role in water retention against environmental desiccation stress; however, the mechanism underlying the role of ApoD in insect desiccation tolerance has not yet been elucidated. Here, we report the molecular constitution, functional analysis, and phylogenetic relationship of the ApoD gene in Acyrthosiphon pisum (ApApoD). We found that ApApoD was transcribed throughout the life cycle of A. pisum, but was prominently expressed in the embryonic period and abdominal cuticle. In addition, we optimized the dose and silencing duration of RNAi, observing that RNAi against ApApoD significantly reduced the levels of both internal and cuticular hydrocarbons and adult fecundity. Moreover, cuticular hydrocarbon deficiency increased the sensitivity of aphids to desiccation stress and reduced their survival time, while desiccation stress significantly increased ApApoD expression. Together, it is confirmed that ApApoD participates in regulating cuticular hydrocarbon content of aphids under desiccation stress and is crucial for aphid reproduction. Therefore, the ApApoD gene of A. pisum may be a potential target for RNAi-based insect pest control due to its involvement in cuticular hydrocarbon accumulation and reproduction.

Parallel Mechanism Composed of Abdominal Cuticles and Muscles Simulates the Complex and Diverse Movements of Honey Bee (Apis mellifera L.) Abdomen.

The abdominal intersegmental structures allow insects, such as honey bees, dragonflies, butterflies, and drosophilae, to complete diverse behavioral movements. In order to reveal how the complex abdominal movements of these insects are produced, we use the honey bee (Apis mellifera L.) as a typical insect to study the relationship between intersegmental structures and abdominal motions. Microstructure observational experiments are performed by using the stereoscope and the scanning electron microscope. We find that a parallel mechanism, composed of abdominal cuticle and muscles between the adjacent segments, produces the complex and diverse movements of the honey bee abdomen. These properties regulate multiple behavioral activities such as waggle dance and flight attitude adjustment. The experimental results demonstrate that it is the joint efforts of the muscles and membranes that connected the adjacent cuticles together. The honey bee abdomen can be waggled, expanded, contracted, and flexed with the actions of the muscles. From the view point of mechanics, a parallel mechanism is evolved from the intersegmental connection structures of the honey bee abdomen. Here, we conduct a kinematic analysis of the parallel mechanism to simulate the intersegmental abdominal motions.

Lipophorin receptor regulates the cuticular hydrocarbon accumulation and adult fecundity of the pea aphid Acyrthosiphon pisum.

Cuticular hydrocarbons form a barrier that protects terrestrial insects from water loss via the epicuticle. Lipophorin loads and transports lipids, including hydrocarbons, from one tissue to another. In some insects, the lipophorin receptor (LpR), which binds to lipophorin and accepts its lipid cargo, is essential for female fecundity because it mediates the incorporation of lipophorin by developing oocytes. However, it is unclear whether LpR is involved in the accumulation of cuticular hydrocarbons and its precise role in aphid reproduction remains unknown. We herein present the results of our molecular characterization, phylogenetic analysis, and functional annotation of the pea aphid (Acyrthosiphon pisum) LpR gene (ApLpR). This gene was transcribed throughout the A. pisum life cycle, but especially during the embryonic stage and in the abdominal cuticle. Furthermore, we optimized the RHA interference (RNAi) parameters by determining the ideal dose and duration for gene silencing in the pea aphid. We observed that the RNAi-based ApLpR suppression significantly decreased the internal and cuticular hydrocarbon contents as well as adult fecundity. Additionally, a deficiency in cuticular hydrocarbons increased the susceptibility of aphids to desiccation stress, with decreased survival rates under simulated drought conditions. Moreover, ApLpR expression levels significantly increased in response to the desiccation treatment. These results confirm that ApLpR is involved in transporting hydrocarbons and protecting aphids from desiccation stress. Furthermore, this gene is vital for aphid reproduction. Therefore, the ApLpR gene of A. pisum may be a novel RNAi target relevant for insect pest management.